How does a non-return valve work on a boiler?
The main function of a non-return valve (NRV), otherwise known as stop or check valve, is to allow steam flow in one direction, and automatically prevent backflow. In other words, they prevent steam from flowing back to the main header of the boiler, or back to a boiler that has failed or is off-line.
Where is the non-return valve on a boiler?
The non-return valve, also called a stop check valve, is usually positioned on a pipe between the boiler and the feed pump. Through this valve, hot water vapor from the boiler can be stopped or started. It consists of a disc and a stem, and it can be closed by turning down the stem and shutting off the flow.
How does a fuel non-return valve work?
Non-return valves work by allowing media to flow through them in only one direction. These valves have two openings in the body, one for media to enter and the other for media to leave. Non-return valves work automatically, which means that most are not controlled by a person or an external control.
What happens when non-return valve fails?
Symptoms of a Failing Check Valve For example, failing check valves will start to vibrate and even lose some internal parts when problems begin to arise. Other symptoms of check valve failure include reverse flow and excessive component wear and damage. Check valves will also emit noises as they start to break down.
Are non return valves required?
So whilst there’s nothing at all wrong with non-return valves, which serve a useful purpose in preventing reverse flow in pipes, they are the wrong fittings where there is a legal requirement for a recognised backflow prevention device.
How do you find a non return valve?
The non-return valve should have a cross sign (✖️) on the head of the spindle, seeing this you can easily figure out that the one with a cross sign is the non-return type.
What is the purpose of non-return valve?
A non-return valve allows a medium to flow in only one direction and is fitted to ensure that the medium flows through a pipe in the right direction, where pressure conditions may otherwise cause reversed flow.
Can you close a non-return valve?
Stop check non-return valves “Stop check NRVs have an override control to stop the flow, regardless of flow direction or pressure”, discusses Scott. “As well as closing in response to insufficient forward pressure or backflow, stop check non-return valves can also be deliberately shut off by an external mechanism”.
Why do non-return valves fail?
This is a common problem in many old systems where valves are generally not spring-loaded or motor-operated. In short, the non-return valve closure (during pump operation changeover), resulting in the water hammer in the pipe line, is likely to be the main root cause of the pump’s frequent failure.